Tin II Chloride Structure Preparation Properties and Uses

SnCl₂ is a crystalline mass with the chemical name Tin (II) Chloride in its solid form. The chemical name of Stannous Chloride is Tin (II) Chloride. It is also known as Tin Dichloride, Dichlorotin, Dichlorostannate, and Tin protochloride. It is an easily available compound and remains in solid form at room temperature. As the formula suggests, one molecule of Tin (II) Chloride has one atom of tin and two atoms of Chlorine. It is highly toxic in nature and may cause irritation and redness in the eyes and throat. It is used as a reducing agent, in the manufacturing of medicines, in the production of dyes, and for tin plating. From being a mordant in the dyeing industry to being a food additive in the food industry, it is one of the most versatile compounds.

Key Terms: Tin (II) Chloride, Stannous Chloride, Ionic Compound, Covalent Compound, Crystalline Solid, Stannous Chloride Dihydrate, Reducing Agent, Hydrolysis, Tin Plating

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Structure of SnCl₂

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The structure of Stannous Chloride is given below:

Structure of SnCl₂

As one can see from the given structures, in a molecule of Stannous Chloride, the central atom of tin is bonded to two chlorine atoms by ionic bonds. The lone pair of electrons present on the central tin atom causes the shrinkage of the bond angle between the chloride atoms to 85°. This is on account of the repulsive forces due to the bond pair and the lone pair interactions. In gaseous form, Stannous Chloride has a bent or V-shaped structure.

In the crystal lattice, Stannous chloride exhibits orthorhombic cubic unit cells and occurs as chains linked via chloride bridges.

In an aqueous solution, SnCl₂ forms SnCl₂ dihydrate. This dihydrate is a three co-ordinated structure, with one molecule of water co-ordinated to a tin atom and the second molecule of water co-ordinated to the first molecule of water.

Read More: Types of Solutions

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Preparation of SnCl₂

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The various methods of preparation of SnCl₂ are as follows:

• Anhydrous Tin (II) Chloride is prepared by subjecting hot tin to dry HCl gas. It is an example of a displacement reaction, the position of tin is above hydrogen in the reactivity series of metals and so tin displaces hydrogen from HCl to form Tin(II) Chloride. Hydrogen, being a gaseous by-product, escapes from the leaving anhydrous SnCl₂ behind.

Sn (s) + 2HCl → SnCl₂ + H₂ (g)

• Another method of preparation is heating tin with mercuric chloride. It is an alternative method used in the preparation of anhydrous SnCl₂. Here, the by-product obtained is mercury (Hg).

Sn + HgCl₂ → Hg + SnCl₂

• Stannous chloride dihydrate (solution) is obtained by heating Stannous oxide or Stannous hydroxide with concentrated HCl in the presence of water (in the case of stannous oxide). Solid crystals can be obtained upon evaporation of the obtained product.

SnO + 2HCl + H₂O → SnCl₂.2H₂O

Sn(OH)₂ + 2HCl → SnCl₂.2H₂O

• Anhydrous Stannous dihydrate cannot be prepared by directly heating an aqueous solution of Stannous Chloride as it leads to the formation of Stannous oxochloride. 

SnCl₂.2H₂O → HCl + Sn(OH)Cl + H₂O

Stannous Chloride

Read More: Ammonium Chloride- Properties, Preparation, Uses

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Physical Properties of SnCl₂

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Stannous Chloride is a white crystalline solid in anhydrous form. It is hygroscopic in nature and on coming in contact with moisture it dissolves to give Stannous Chloride dihydrate. It is odourless and appears colourless in solution. 

It is a very toxic and hazardous compound. When inhaled it causes severe irritation and a burning sensation in the nasal passage and throat. It may cause death if ingested in moderate amounts.

Its molecular mass is 189 g/mol. Stannous Chloride has a very high boiling point (623°C) and high melting point (247°C).

The Physical properties of Stannous Chloride are summarized in the table given below:-

Read More: Classification of Crystalline Solids

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Chemical Properties of SnCl₂

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The chemical properties and reactions of SnCl₂ are listed below: 

• Reaction with water: Stannous Chloride is hydrolysed in the presence of excessive water to form tin oxochloride.

SnCl₂ (aq) + H₂O (l) → Sn(OH)Cl (s) + HCl (aq)

• Reaction with Mercuric Chloride: SnCl4 can be obtained by treating Stannous Chloride SnCl2 with mercuric chloride.

SnCl₂ + 2HgCl₂ → SnCl₄ + Hg₂Cl₂

Hg₂Cl₂ + SnCl₂ → SnCl₄ + 2Hg

• Reduction of Ferric Chloride to Ferrous Chloride: It reduces ferric chloride to ferrous chloride. Stannous chloride is a good reducing agent as it readily donates a pair of electrons to get oxidised to SnCl4.

2FeCl₃ + SnCl₂ → 2FeCl₂ + SnCl₄

• Reduction of Iodine: In the presence of dil. HCl acid Stannous Chloride reduces Iodine to hydrogen iodide. Here also stannous chloride gets oxidised to stannic chloride.

I₂ + 2HCl + SnCl₂ → SnCl₄ + 2HI

• Reaction with Alkalis: It reacts with hydroxides of sodium and potassium to give the corresponding stannate, water and the corresponding chloride salt.

SnCl₂ + 4NaOH → 2NaCl + 2H₂O + Na₂SnO₂

• Reaction with Hydrogen Sulphide: Black precipitate of stannous sulphide is obtained when hydrogen sulphide gas flows in the stannous chloride solution, which dissolves in the yellow ammonium sulphide solution. This reaction of stannous chloride with hydrogen sulphide serves as a test to detect the presence of stannous chloride in a compound.

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Uses of SnCl₂

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The major uses of SnCl2 are as follows: 

• As a lab reagent: Stannous Chloride is an excellent reducing agent and hence it is used extensively as a lab reagent to carry out some commercially important reduction reactions. One such example is the use of Stannous Chloride in Stephen's reduction of organic compounds and also in Son–Muller method.
• As a food additive: Stannous Chloride is used in a number of canned and processed foods as an antioxidant as well as for its colour retention ability.
• As mordant in the dyeing industry: A mordant is a substance that helps attach the colour to get strongly attached to the fibres of the fabrics. In this case, Tin chloride (II) forms a coordination complex with the dye to attach the dye particles to the fabric.
• Silvering of mirrors: Another common application of Stannous chloride is the silvering of mirrors. In this process, tin is deposited on the glass surface to make a reflecting surface.
• Tin plating: Stannous Chloride is used in the electroplating of steel as it is a cheaper alternative to silver deposition.
• Pharmaceuticals: Stannous Chloride is used in the production of a number of medicines.
• It is used for the removal of ink stains.
• Catalyst: It acts as a catalyst in the production of plastic polylactic acid.

Read More: Amorphous and Crystalline Solids

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Things to Remember

• Stannous chloride is an odourless white crystalline solid which is easily soluble in water. 
• The oxidation state of tin in the Stannous Chloride is +2. It is an ionic compound and a good conductor of electricity in its aqueous solution.
• In the gaseous phase, Stannous Chloride has a V-shaped molecular structure and the bond angle between the chlorine atoms is 85°, while in the solid-state the molecules are joined together as chains through chlorine bridges.
• Stannous Chloride can be easily prepared by treating HCl with hot tin. It can also be prepared with mercuric chloride and tin.
• It has a high melting and boiling point and it is hygroscopic in nature.
• Stannous chloride is a good reducing agent and reduces ferric chloride to ferrous chloride. It also reduces Iodine to hydrogen iodide.
• It hydrolyses easily in excessive water to give tin oxochloride.
• It is used as a reducing agent, silvering of mirrors, as a food additive and as tin plating of silver. 

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